Thursday, June 07, 2018

The frequency of high-tide flooding has doubled in 30 years. Some cities faced more than 20 days of it in the past year, and not just during hurricanes.

The nation's coasts broke records for tidal flooding over the past year as storms combined with rising seas to inundate downtown areas of Miami, Boston, and other major cities, according to a federal report released Wednesday.While some of the flooding coincided with hurricanes and nor'easters, much of it was driven mainly by sea level rise fueled by climate change, scientists with the National Oceanographic and Atmospheric Administration (NOAA) write.The oceans are rising about 3 millimeters a year on average, driven primarily by melting land ice and warming water, which expands. That rate is accelerating, and it has led to a steady increase in U.S. coastal flooding in recent decades, the report shows. Several cities—including Boston, Atlantic City, and Sabine Pass, Texas—saw more than 20 days of high-tide flooding between May 2017 and April 2018, the "meteorological year" covered by the report."Though year‐to‐year and regional variability exist, the underlying trend is quite clear," the report says. "Due to sea level rise, the national average frequency of high tide flooding is double what it was 30 years ago."Building Barriers in Boston: Costs Add UpWhile many cities are beginning to address the threat posed by rising seas, the findings highlight the fact that they aren't keeping pace with the problem.Boston is two years into a city-wide initiative to protect itself from the effects of climate change, including rising seas. It has begun efforts to shield some vulnerable areas by building new flood walls and elevating streets. Another proposal envisions a harbor-wide barrier system that would close during major storms and cost billions of dollars. But last week, a city-backed study recommended against building a barrier, saying the money would be better spent on smaller-scale measures, such as flood walls or green infrastructure.

A series of winter storms this year underscored the urgency of the problem: Boston matched its previous 12-month record, set in 2009, with 22 days of tidal flooding from May through April. One of those storms, in January, led to the highest tide ever recorded in the city and pushed seawater through downtown streets.